The study of motion of liquids and gases is an important practical subject that finds applications in various fields like aeronautics, meteorology, marine engineering, and civil engineering. Liquids under flow obey the same fundamental laws as followed by particles, however, special formulations are necessary to save time. Further, as the description of the motion of real liquids often leads to complexities, in the beginning, we shall consider the flow of liquids under certain simplifying assumptions. We shall assume that-
the flow is steady.
the liquid is incompressible.
the liquid is non-viscous.
A flow is said to be steady if the fluid velocity at a point does not change with time and the statement holds for all the points.
Thus in a steady flow ν is independent of time although it may depend on the position. Every small element of liquid which arrives at a particular point, therefore, follows a prescribed path. We call this path a streamline.
A streamline is a line drawn such that at each point its direction is the direction of the fluid velocity at that point.
In a steady flow, streamlines are stationary and they do not cut each other. However, if it is not so we say that the flow is turbulent. Steady flow occurs at low speeds.
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